Radio communication station and radio communication device, and methods of operating same

ABSTRACT

A radio communication station in a radio communication system having a plurality of radio communication devices, derives a quantisation parameter and transmits the quantisation parameter to the radio communication devices for use in subsequent quantisation of a channel state metric. The radio communication devices receive the quantisation parameter, determine a channel state metric, quantise the determined channel state metric by applying quantisation ranges indicated by the quantisation parameter, determine a data value indicative of the quantised channel state metric, and transmit a signal conveying the determined data value as a random access transmission.

This application is a Division of application Ser. No. 12/376581 filed Feb. 6, 2009 which is a National Phase Application under 35 CFR 371 of International Application PCT/IB2007/053145 filed Aug. 8, 2007 and claims foreign priority of EPO 06118696.1 filed Aug. 9, 2006.

The invention relates to a radio communication apparatus and to a method of operating a radio communication apparatus. The invention has application in, for example but not exclusively, mobile communication systems.

Mobile communication systems typically incorporate mechanisms to transmit information about the state of a radio channel. For example, channel state information can be sent as part of the random access mechanism by which mobile terminals can access a network. In one example of a random access mechanism which is under consideration for the UMTS LTE (Universal Mobile Telecommunication System Long Term Evolution) a mobile terminal transmits a signature on an asynchronous random access channel (RACH). The mobile terminal selects a particular signature from a larger set (e.g. of 64), which enables a few bits (e.g. 6) of information to be conveyed. One requirement is that the collision probability (i.e. probability that two mobile terminals use the same signature at the same time) should be sufficiently low. A further requirement is that the resulting waveforms have low cross-correlation.

The bit pattern defining the signature can be considered in terms of one or more data fields. Some examples of the potential contents of the data fields are:

-   -   Pseudo-random data (in the form of a temporary mobile terminal         identity to reduce the risk of collision)     -   Channel quality indicator (CQI) or pathloss measurement     -   Reason for RACH access         The CQI and Reason fields may also help to reduce collisions if         they are sufficiently uncorrelated between terminals.

The example mechanism described above suffers from competing problems of the limited number of useful data bits which can be sent, and the potential collision probability.

An object of the invention is to enable an improved random access mechanism.

According to a first aspect of the invention there is provided a method of operating a radio communication station in a radio communication system having a plurality of radio communication devices, comprising deriving a quantisation parameter and transmitting the quantisation parameter to the radio communication devices for use in subsequent quantisation of a channel state metric.

According to a second aspect of the invention there is provided a method of operating a radio communication device, comprising: receiving a quantisation parameter; determining a channel state metric; quantising the determined channel state metric by applying quantisation ranges indicated by the quantisation parameter; determining a data value indicative of the quantised channel state metric; and transmitting a signal conveying the determined data value as a random access transmission.

The invention also provides a method of operating a communication system comprising operating a radio communication station in accordance with the first aspect of the invention and operating a radio communication device in accordance with the second aspect of the invention.

According to a third aspect of the invention there is provided a radio communication station for use in a radio communication system having a plurality of radio communication devices, comprising means adapted to derive a quantisation parameter and means adapted to transmit the quantisation parameter to the radio communication devices for use in subsequent quantisation of a channel state metric.

According to a fourth aspect of the invention there is provided a radio communication device, comprising: means adapted to receive a quantisation parameter; means adapted to determine a channel state metric; means adapted to quantise the determined channel state metric by applying quantisation ranges indicated by the quantisation parameter; means adapted to determine a data value indicative of the quantised channel state metric; and means adapted to transmit a signal conveying the determined data value as a random access transmission.

The invention also provides a communication system comprising a radio communication station in accordance with the third aspect of the invention and a radio communication device in accordance with the fourth aspect of the invention.

Depending on the probability density function (PDF) of channel state metric values, and consequently of the data values, the collision probability may be higher than if random data alone was transmitted. In contrast to the invention, a fixed quantisation algorithm for quantising the data bits does not adapt to changes in the distribution of measured channel state metric values, and may therefore result in a high collision probability if a significant proportion of the mobile terminals measure substantially-similar values. The present invention alleviates this problem by enabling the quantisation algorithm to be adapted.

The quantisation parameter may be derived dependent on a characteristic of the radio communication system. This enables the radio communication station to adapt the quantisation parameter to time-varying system characteristics.

The characteristic of the radio communication system may be derived from signals received on a random access channel from a plurality of radio communication devices. This enables the radio communication station to adapt the quantisation parameter to, for example, the activity level and signal quality of the radio communication devices.

The signals received on the random access channel from the plurality of radio communication devices, may each convey a data value indicative of a quantised channel state metric of the respective radio communication device, and the radio communication station may derive the quantisation parameter dependent on the data values. This enables the radio communication station to adapt the quantisation parameter to the channel state metrics. Different sets of data values may be conveyed by different time and/or frequency resource slots.

The radio communication station may derive the quantisation parameter dependent, for example, on the frequency of occurrence of different data values. This enables the radio communication station to adapt the quantisation parameter to control the number of collisions of the signals transmitted by the radio communication devices. In particular the quantisation parameter may be adjusted to reduce the frequency of occurrence of the most frequently occurring data values, thereby reducing the number of collisions.

The quantisation parameter may be indicative of quantisation ranges at least some of which have unequal width. This also enables the number of collisions to be controlled.

Different data values may be conveyed by different time and/or frequency resource slots. The different resource slots may correspond to quantisation ranges having different widths. These features also enable the number of collisions to be controlled.

The channel state metric may be indicative of one or more of:

-   channel quality indicator for a received signal; -   channel transfer function; -   channel quality indicators for more than one frequency or frequency     band; -   channel quality indicators for more than one antenna; -   average value of a channel quality indicators for more than one     antenna; -   difference between channel quality indicators for more than one     antenna; -   location of the radio communication device; -   angle of a receive path; -   requested data rate.

A channel quality indicator may, for example, comprise one or more of:

-   a signal to noise ratio; -   a signal to interference ratio; -   a receiveable data rate; -   a path loss.

The invention will now be described, by way of example only, with reference to the accompanying drawings wherein;

FIG. 1 is an example PDF of CQI values and ideal quantisation thresholds for maximum randomisation of transmitted values;

FIG. 2 is a table of example quantisation ranges and corresponding data values;

FIG. 3 is an example PDF for unequal quantisation ranges; and

FIG. 4 illustrates another example of quantisation thresholds.

MODES FOR CARRYING OUT THE INVENTION

Embodiments of the invention will be described with reference to a mobile communication system in which the radio communication device may be a mobile terminal, such as a mobile phone, and the radio communication station may be a base station in a network.

According to the invention, at least one quantisation parameter for quantising data to be transmitted in a random access preamble is signalled to a mobile terminal. When the mobile terminal quantises data in accordance with the signalled parameter(s), the probability of occurrence of each of the data values that can be signalled in the preamble can be made more similar.

In general, according to the invention at least part of the data transmitted in the preamble signature would typically be non-uniformly quantised. The non-uniform quantisation would be designed to give a more uniform distribution of transmitted data values than would be the case with a uniform quantisation, based on an assumed or estimated PDF of the data to be transmitted. This reduces the risk of signature collisions between the RACH attempts of different mobile terminals. This improvement is accompanied by a reduction in the resolution of the transmitted data around the least-probable ranges of values.

In a simple embodiment, the signalled quantisation parameter may comprise the highest and lowest quantisation levels to be used. This would indicate that all measured values above the highest quantisation level or below the lowest quantisation level would be sent with the highest or lowest data value respectively.

Quantisation in the region between the highest and lowest levels could be carried out using a predetermined granularity, for example determined by the number of bits available for data transmission.

For example, FIG. 1 shows an example of a PDF of CQI values which may, for example, be assumed to follow a log-normal distribution. In this case, the quantisation thresholds for mapping CQI values to data bits to be transmitted in the preamble are ideally selected so as to give a substantially uniform distribution of the data bits to be transmitted. FIG. 1 shows where the quantisation levels would be placed following this ideal assumption; the mapping shown in FIG. 2 would be used between the CQI value in dB and the signalled data bits, for a case when 3 bits are used to represent CQI in the preamble signature.

It can be seen from FIG. 1 that the quantisation thresholds are substantially evenly-spaced within a limited range of the full set of values.

An approximation to this quantisation pattern is to apply evenly-spaced thresholds between the highest and lowest thresholds. For example, in the simple embodiment described above, highest and lowest thresholds of 19.5 dB and 10.5 dB respectively would be signalled to the mobile terminals.

Knowing the number of bits available for data reporting (in this example 3), and hence the fact that 8 data values are available, the mobile terminal can then position equidistantly intermediate thresholds at 12 dB, 13.5 dB, 15 dB, 16.5 dB and 18 dB. This results in the probabilities of transmission of each of the available data values being as shown in FIG. 3.

More advanced embodiments can include the signalling of additional parameters. For example:

-   -   The levels of more than two of the quantisation thresholds could         be signalled to the mobile terminals, together with an indicator         of the number of quantisation thresholds (or bands), or the         quantisation threshold spacing, between each of the signalled         thresholds.     -   More advanced functions of the quantisation threshold spacing         could also be signalled between one or more pairs of the         signalled quantisation thresholds. For example, the gradient of         the quantisation threshold spacing could be signalled, or the         coefficients of a polynomial function of the quantisation         threshold spacing.

A further example is shown in FIG. 4, where the values of three quantisation thresholds are signalled to the mobile terminals, together with indicators that a 1 dB spacing should be used for the quantisation thresholds between the first and second signalled quantisation thresholds and a 2 dB spacing should be used for the quantisation thresholds between the second and third signalled quantisation thresholds.

The quantisation parameter selection shown in FIG. 4 can, for example, take into account the fact that it may be desirable, in the case of CQI reporting, to report CQI values more accurately at low values of SINR (signal to interference and noise ratio) than at higher values.

Thus the exact choice of quantisation parameters can be based on a combination of the aim of randomising the transmitted data values to minimise collision probability, and consideration of the effect of higher or lower degrees of accuracy in the data values.

The quantisation parameter(s) may be selected according to the deployment scenario (e.g. indoor, outdoor or macro/pico cell), or current traffic conditions.

The invention may also be applied to other kinds of information than CQI (including further channel state metrics). For example:

-   -   Channel transfer function     -   CQI for more than one frequency or frequency band     -   CQI for more than one antenna     -   Average CQI for more than one antenna     -   Different CQI between antennas     -   Location of the UE     -   Angle of the path from the UE to the access point     -   Required data rate

The signalling of quantisation parameters may be configurable (e.g. only applied under high loading conditions, when collisions are more likely).

The signalling of the quantisation parameters may be updated according to measurements of the PDF of data received in actual preambles.

The quantisation parameter(s) may be derived dependent on, for example:

-   -   CQI reports transmitted on different channels     -   current cell size     -   handover measurements

In the present specification and claims the word “a” or “an” preceding an element does not exclude the presence of a plurality of such elements. Further, the word “comprising” does not exclude the presence of other elements or steps than those listed.

The inclusion of reference signs in parentheses in the claims is intended to aid understanding and is not intended to be limiting.

From reading the present disclosure, other modifications will be apparent to persons skilled in the art. Such modifications may involve other features which are already known in the art of radio communication and which may be used instead of or in addition to features already described herein.

INDUSTRIAL APPLICABILITY

Wireless communication systems, for example UMTS LTE or other cellular systems such as UMTS WCDMA (Wideband Code Division Multiple Access). 

1. A method of operating a radio communication station in a radio communication system having a plurality of radio communication devices, comprising: receiving signals on a random access channel from the plurality of radio communication devices; deriving a characteristic of the radio communication system from the received signals; deriving a quantization parameter depending on the characteristic; and transmitting the quantization parameter to the plurality of radio communication devices for use in subsequent quantization of a channel state metric.
 2. The method of claim 1, wherein the received signals received on the random access channel convey data values indicative of a channel state metric quantized with a previous quantization parameter.
 3. The method of claim 1, wherein each of said signals received on the random access channel convey a data value indicative of a quantized channel state metric of a respective one of the plurality of radio communication devices.
 4. The method of claim 3, wherein deriving a characteristic of the radio communication system comprises deriving the data values from the signals received on the random access channel.
 5. The method of claim 4, wherein deriving the quantization parameter depending on a characteristic of the radio communication system comprises deriving the quantization parameter depending on the data values.
 6. The method of claim 3, wherein deriving the quantization parameter is dependent on the frequency of occurrence of different data values.
 7. The method of claim 6, wherein the quantization parameter is adjusted to reduce the frequency of occurrence of the most frequently occurring data values.
 8. The method of claim 3, wherein different sets of data values are conveyed by different time and/or frequency resource slots to the radio communication station.
 9. The method of claim 1, wherein the quantization parameter is indicative of a threshold.
 10. The method of claim 1, wherein the quantization parameter is indicative of quantization ranges at least some of which have unequal width.
 11. A method of operating a radio communication device in a radio communication system having a radio communication station, the method comprising: receiving a quantization parameter from the radio communication station; determining a channel state metric; quantizing the determined channel state metric by applying quantization ranges indicated by the quantization parameter; determining a data value indicative of the quantized channel state metric; and transmitting a signal conveying the determined data value as a random access transmission to the radio communication station.
 12. The method of claim 11, wherein the transmitted signal that conveys the determined data values is indicative of the channel state metric quantized with the quantization parameter.
 13. The method of claim 11 wherein the received quantization parameter is derived by a radio communication station depending on the frequency of occurrence of different previous data values from different respective radio communication devices, and wherein the received quantization parameter is adjusted by a radio communication station to reduce the frequency of occurrence of the most frequently occurring data values, and wherein the radio communication station transmits the quantization parameter to the radio communication device.
 14. A method of claim 11, wherein different data values of different radio communication devices are conveyed by different time and/or frequency resource slots to the radio communication station.
 15. The method of claim 11, wherein the quantization parameter is indicative of a threshold, and comprising the act of: if the value of the channel state metric falls above the threshold, transmitting the signal conveying the data values in a first time and/or frequency resource slot; and, if the value of the channel state metric falls below the threshold, transmitting the signal conveying the data values in a second time and/or frequency resource slot.
 16. The method of claim 11, wherein at least some of the quantization ranges have unequal width.
 17. The method of claim 11, wherein the channel state metric is indicative of one or more of: channel quality indicator for a received signal; channel transfer function; channel quality indicators for more than one frequency or frequency band; channel quality indicators for more than one antenna; average value of a channel quality indicators for more than one antenna; difference between channel quality indicators for more than one antenna; location of the radio communication device; angle of a receive path; requested data rate; receivable data rate; path loss; signal to noise ratio; signal to interference ratio.
 18. A method of operating a communication system having a radio communication station and a plurality of radio communication devices, comprising the steps of: the radio communication station deriving a quantization parameter; the radio communication station transmitting the quantization parameter to the radio communication devices; the radio communication devices each receiving the quantization parameter; the radio communication devices each determining a respective channel state metric; the radio communication devices each quantizing the determined channel state metric by applying quantization ranges indicated by the quantization parameter; the radio communication devices each determining a data value indicative of the quantized channel state metric; and the radio communication devices each transmitting a signal conveying the determined data value as a random access transmission to the radio communication station.
 19. The method of claim 18 comprising: the radio communications station receiving a signal on a random access channel from each respective radio communication device of the plurality of radio communication devices, the signals conveying data values indicative of a channel metric quantized with a previous quantization parameter; the radio communications station deriving the data values from the signals received on the random access channel; the radio communications station wherein the quantization parameter is derived depending on the data values and depending on the frequency of occurrence of different data values; and the radio communications station adjusting the quantization parameter to reduce the frequency of occurrence of the most frequently occurring data values.
 20. A radio communication station for use in a radio communication system having a plurality of radio communication devices, comprising: means adapted to derive a quantization parameter; and means adapted to transmit the quantization parameter to the radio communication devices for use in subsequent quantization of a channel state metric.
 21. The radio communication station of claim 20, comprising means adopted to receive signals on a random access channel from the plurality of radio communication devices.
 22. The radio communication station of claim 21, comprising means adopted to derive a characteristic of the radio communication system from the received signals; and wherein deriving the quantization parameter is depending on the characteristic.
 23. The radio communication station of claim 22, wherein the signals received on the random access channel each convey a data value indicative of a quantized channel state metric of a respective one of the plurality of radio communication devices.
 24. A radio communication station of claim 23, comprising means adapted to derive the data values from the signals received on the random access channel.
 25. A radio communication station of claim 24, wherein deriving the quantization parameter depends on the data values.
 26. A radio communication station of claim 25, wherein deriving the quantization parameter depends on the frequency of occurrence of different data values.
 27. A radio communication station of claim 26, comprising means adapted to repeatedly adjust the quantization parameter to reduce the frequency of occurrence of the most frequently occurring data values.
 28. The radio communication station of claim 25, comprising means adapted to determine different sets of data values from different time and/or frequency resource slots.
 29. The radio communication station of claim 20, wherein the quantization parameter is indicative of a threshold.
 30. The radio communication station of claim 20, wherein the quantization parameter is indicative of quantization ranges at least some of which have unequal width.
 31. A radio communication device for operation in a radio communication system having a radio communication station and a plurality of radio communication devices, comprising: means adapted to receive a quantization parameter; means adapted to determine a channel state metric; means adapted to quantize the determined channel state metric by applying quantization ranges indicated by the quantization parameter; means adapted to determine a data value indicative of the quantized channel state metric; and means adapted to transmit a signal conveying the determined data value as a random access transmission.
 32. The radio communication device of claim 31 wherein the quantization parameter is derived depending on the frequency of occurrence of different data values, and wherein the quantization parameter is adjusted to reduce the frequency of occurrence of the most frequently occurring data values.
 33. A radio communication device of claim 31, comprising means adapted to convey different data values by transmitting the signal in different time and/or frequency resource slots.
 34. The radio communication device of claim 31, wherein the quantization parameter is indicative of a threshold, and wherein the means adapted to transmit is further adapted to: if the value of the channel state metric falls above the threshold, transmit the signal conveying the data values in a first time and/or frequency resource slot; and if the value of the channel state metric falls below the threshold, transmit the signal conveying the data values in a second time and/or frequency resource slot.
 35. The radio communication device of claim 31, wherein at least some of the quantization ranges have unequal width.
 36. The radio communication device of claim 31, wherein the channel state metric is indicative of one or more of: channel quality indicator for a received signal; channel transfer function; channel quality indicators for more than one frequency or frequency band; channel quality indicators for more than one antenna; average value of a channel quality indicators for more than one antenna; difference between channel quality indicators for more than one antenna; location of the radio communication device; angle of a receive path; requested data rate; receivable data rate; path loss; signal to noise ratio; signal to interference ratio.
 37. A radio communication system having a radio communication station and a plurality of radio communication devices, comprising: derivation means adapted to derive a quantization parameter in the radio communication station; parameter transmission means adapted to transmit the quantization parameter from the radio communication station to the radio communication devices for use in subsequent quantization of a channel state metric; device receiving means adapted to receive a quantization parameter into a radio communication device; determination means adapted to determine a channel state metric of the radio communication device; quantization means adapted to quantize the determined channel state metric by applying quantization ranges indicated by the quantization parameter received by the radio communication device; data determination means adapted to determine a data value indicative of the quantized channel state metric of the radio communication device; and transmission means adapted to transmit a signal conveying the determined data value as a random access transmission.
 38. The system of claim 37, wherein the quantization parameter is derived depending on a characteristic of the radio communication system.
 39. The system of claim 38, wherein the characteristic of the radio communication system is derived from signals received on a random access channel from a plurality of radio communication devices.
 40. The system of claim 39, wherein the signals received on the random access channel each convey a data value indicative of a quantized channel state metric of the respective radio communication device, the system comprises means adapted to derive the data values from the signals received on the random access channel and wherein deriving the quantization parameter depending on a characteristic of the radio communication system comprises deriving the quantization parameter depending on the data values.
 41. A method of operating a radio communication station in a radio communication system having a plurality of radio communication devices, the method comprising: deriving a quantization parameter depending on the frequency of occurrence of different data values, the deriving includes adjusting the quantization parameter to reduce the frequency of occurrence of the most frequently occurring data values; transmitting the quantization parameter to the radio communication devices for use in subsequent quantization of a channel state metric; and receiving signals as random access transmissions from the plurality of radio communication devices, the signals conveying data values indicative of a channel metric quantized with the quantization parameter.
 42. The method of claim 41, comprising deriving the data values from the signals.
 43. The method of claim 41, wherein different sets of data values are conveyed by different time and/or frequency resource slots to the radio communication station.
 44. The method of claim 41, wherein the quantization parameter is indicative of a threshold.
 45. The method of claim 41, wherein the quantization parameter is indicative of quantization ranges at least some of which have unequal width. 